1. Field of the Invention
The present invention relates to electronic and electrical systems. More specifically, the present invention relates to systems and methods for electronic circuit and component protection.
2. Description of the Related Art
In many applications, there is a need for a scheme for protecting an electronic circuit from ambient radiation. One such application involves the use of radar-guided weapons. Radar-guided weapons such as Small Diameter Bomb II (SDB-II) will make many flights while strapped to the wing of an aircraft, in an un-powered (passive) state. As the aircraft takes off and lands or is parked, there is no way to control the illumination that might be present due to other radars, and the weapon should protect itself so that no damage is inflicted. A prediction of the maximum signal strength environment that systems such as SDB-II might experience is shown in FIG. 1.
There are two regions on the curve that severely stress the system. These are approximately Ku-band: 120 W peak, 600 mW average and Ka-band: 100 W peak, 2 watts average.
However, the analysis provides only an estimate that may prove to be optimistic. A goal for a protection system might be to harden the front-end to 1000 watts peak, 10 watts average, at any frequency from X through Ka-band. It should be noted that typical stray radar signals are high peak power but low average power.
A radar guided weapon front-end typically employs a combination of passive and active circuitry to provide required transmit power and set system noise figure. The active components should be protected, or “hardened” from stray radiation. The protection device should be provided in front of the active circuitry. It should act passively, to protect the system in the absence of prime power. When the system is turned on, the protection system should have a minimal effect on transceiver performance, i.e. it should not severely degrade output power during transmit or noise figure during receive. Ideally, the protection system will have minimal impact on radar figure of merit (FOM), the ratio of transmit output power to receive noise figure of the radar.
There are four major characteristics that are important for passive protection: 1) size; 2) cost; 3) effect on transceiver performance, i.e., minimize hit on radar figure of merit; and 4) protection power level and bandwidth.
A conventional method for passive protection involves the use of PIN diode limiters. PIN diode limiters can be an effective solution with respect to the above-noted desirable characteristics at X-band. PIN diode limiters can be made to handle enormous power levels but the bandwidth of PIN diode limiters is limited. However, future radar guided weapons may operate at Ka-band. The typical insertion loss of a 1000 peak watt PIN diode limiter at Ka-band may yield a radar figure of merit that is unacceptable for future requirements. Thus, there is a need for an improved passive protection system that operates at Ka-band frequencies and maintains the highest performance FOM.
Prior approaches for passive protection have primarily involved X-band missiles. The conventional X-band solution is to employ passive limiters at the front-end of the active electronics.
In this conventional approach, the first component that is seen by a received signal that passes from antenna to comparator network to transceiver is a passive limiter. Because of the nature of the comparator network, it is possible that the vast majority of a stray radar signal that uniformly illuminates the antenna may combine at a single transceiver channel, most likely the SUM channel. Therefore a typical 1000 watt peak uniform-illumination input to the antenna/feed requires that each transceiver input should be hardened to withstand 1000 watts peak if the feed and comparator network are considered lossless.
While schemes have been developed to make the PIN diode approach work for X-band radiation, the mere fact that PIN diode passive protection schemes can be made to work well for X-band does not provide a solution that is ideal for Ka-band. That is, the loss of a high-power limiter for a given protection level increases with center frequency. Hence, a solution that only affects radar FOM by one dB at X-band might surpass 3 dB at 35 GHz, which is an unacceptable solution for future applications.
Protective shrouds placed over the antenna have been considered, however, this approach is cumbersome and adds cost and weight to the system.
Hence, a need remains in the art for a system or method for protecting antenna feed networks and other sensitive electronic devices from stray radiation and other adverse electromagnetic fields.